1. Field of the Invention
This invention relates to a compact (e.g., hand held) vacuum generator having particular application in pulling a vacuum within the evaporative fuel emissions system (e.g., a gas tank) of a motor vehicle so that a vacuum-decay test can be performed to test the system for leaks while mitigating the hazardous effects of potentially explosive hydrocarbon vapors.
2. Background Art
Vacuum generating devices have been in use for many years. One example of a commercially available vacuum generating device is a hand operated vacuum pump sold under the trademark MITYVAC. Other commonly used vacuum producing devices include electric vacuum pumps designed to evacuate a variety of closed systems, such as an air conditioner refrigeration system of a motor vehicle or a commercial air conditioning system.
When the evaporative emissions system of a motor vehicle is to be tested for leaks by first creating a vacuum, the aforementioned hand operated vacuum pump has usually been employed because electric vacuum pumps are often known to draw excessive vacuum from a system under test. The vacuum force created by electric vacuum pumps is sometimes so large as to possibly collapse the evaporative emissions system of the motor vehicle under test. However, one common problem with using the typical hand operated vacuum pump for leak testing the evaporative emissions system of a motor vehicle is that a time delay of approximately 5 to 10 minutes is required to evacuate the system in order to be able to test the rate of leak. Another problem which is often faced by those performing the leak test is that the vapors which evacuate from the hand operated pump are flammable and could lead to a potentially hazardous explosive condition. Yet another problem is that after the hand operated vacuum pump is disconnected from a test port of the evaporative emissions system under test, ambient air is allowed to flow back into the system, thereby creating a potentially explosive mixture. Still another problem with the typical hand operated vacuum pump is that the vacuum level is selected by the technician performing the vacuum test. In one case, the vacuum level that is selected may pull too much vacuum and, consequently, damage the vehicle. In another case, not enough vacuum may be pulled rendering the test inaccurate.
Accordingly, conventional hand operated vacuum pumps may not be suitable for reliably testing the evaporative emissions system of a motor vehicle when a vacuum-decay (or vacuum-decline) method of testing is required. Therefore, what is needed is a testing apparatus that is especially adapted for testing the evaporative emissions system of a motor vehicle by means of vacuum-decay testing. In this regard, the improved apparatus should be capable of completing a test in a timely and safe manner, assuring repeatable results, being capable of not pulling more vacuum than required, and protecting the system under test as well as the technician by mitigating the hazards of handling flammable vapors in the potentially explosive environment of the test.